Hi , thanks for answering 
1 - Nothing else intensive running, just chrome and antivirus really. I can run much larger projects than my own without the problem occurring. The LandscapeMountains map (with the hang glider) runs at a constant 65-70
2 - The project isn’t much larger than what can be seen in the video I linked.
3 - Not a significant amount of particles or materials - eight particle emitters and not a lot of heavy duty material in the scene. I got rid of the emitters and the problem persists.
4 - Framerate is mostly between 115 and 120 and it isn’t affected when the stutter occurs.
5 - link text
6 - I just ran a blank and clean first person project and they were fine, 120 fps.
However, I just ran the Example Project Welcome level and the problem occurs, it’s actually more severe in this smaller map. FPS stays around 100. As soon as I start fraps and play the level again the stuttering does not occur! When I close fraps it happens again, immediately. The stuttering occurs when looking towards the large Unreal “U” symbol and not away from it. When I delete the UE4_Logo static mesh the stuttering does not occur.
If I mouse through to a stutter point and stop moving the image will remain static until I move again. I’ve tried capturing the problem with fraps a number of times but the stuttering usually does not occur when fraps is recording and does not appear in the recordings anyway - maybe this is significant?